Learn Python By Example – Selecting Items In A List With Filters

Selecting Items In A List With Filters

/* Create an list of items denoting the number of soldiers in each regiment, view the list */
regimentSize = (5345, 6436, 3453, 2352, 5212, 6232, 2124, 3425, 1200, 1000, 1211); regimentSize
(5345, 6436, 3453, 2352, 5212, 6232, 2124, 3425, 1200, 1000, 1211)

One-line Method

This line of code does the same thing as the multiline method below, it is just more compact (but also more complicated to understand.

/* Create a list called smallRegiments that filters regimentSize to  
   find all items that fulfill the lambda function (which looks for all items under 2500). */
smallRegiments = list(filter((lambda x: x < 2500), regimentSize)); smallRegiments
[2352, 2124, 1200, 1000, 1211]

Multi-line Method

The ease with interpreting what is happening, I’ve broken down the one-line filter method into multiple steps, one per line of code. This appears below.

/* Create a lambda function that looks for things under 2500 */
lessThan2500Filter = lambda x: x < 2500
/* Filter regimentSize by the lambda function filter */
filteredRegiments = filter(lessThan2500Filter, regimentSize)
/* Convert the filter results into a list */
smallRegiments = list(filteredRegiments)
[2352, 2124, 1200, 1000, 1211]

For Loop Equivalent

This for loop does the same as both methods above, except it uses a for loop.

Create a for loop that go through each item of a list and finds items under 2500

/* Create a variable for the results of the loop to be placed */
smallRegiments_2 = []

/* for each item in regimentSize, */
for x in regimentSize:
    /* look if the item's value is less than 2500 */
    if x < 2500:
        /* if true, add that item to smallRegiments_2 */

/* View the smallRegiment_2 variable */
[2352, 2124, 1200, 1000, 1211]


Python Example for Beginners

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